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United States Pate
3,071,462
Fatented Jan. 1, 1963
1
2
tent to less than 1.0%, both on grounds of obtaining the
alloy elements in solution in the melt, and in producing
a ?nal alloy of single phase, which for the latter reason
3,071,462
MAGNESIUM ALLOYS
Geo?rey Charles Edward Olds, Leicester, England, as
signor to Associated Electrical Industries (Rugby) Lim
should also be free from serious embrittlement. The Zr
and Mn contents of any Mg-Zr-Mn alloys are, therefore,
ited (formerly known as The British Thomson-Houston
interdependent.
Company Limited), London, England, a British com
Furthermore, the preferred maximum Mn content for
an
pNoyDrawing. Filed July 15, 1960, Ser. No. 42,985
a canning material on grounds of neutron absorption
3 Claims. (Cl. 75-168)
economy is about 0.2%.
10
In more detail, the following examples are given of
The present application is a continuation-in-part of
preferred compositions which were found to be basically
application Serial No. 768,062, ?led on October 20, 1958,
single phase alloys.
by me and assigned to the assignee of the present applica
Alloy
( 1): 0.6% Zr, 0.1% Mn, remainder Mg.
tion.
This invention relates to magnesium alloys suitable, 15 Alloy (2): 0.7% Zr, 0.27% Mn, remainder Mg.
inter alia, for use as a canning material for the fuel
The improvement in creep resistance of alloy (1) con
elements of nuclear reactors. For such purpose, the
taining manganese over its parent alloy of Mg—Zr and
alloy initially cast is required to be subjected to mechan
over alloy (A) of lower content of zirconium is shown
ical working whereby it is wrought into a form suitable
by tensile test creep results as follows:'
for the required application. This may be effected by
hot extrusion.
The important mechanical properties required in an
Composition Secondarycreep
alloy to be used as a canning material for uranium fuel
in a thermal nuclear reactor are high creep ductility be
rate at 1,000
Alloy
tween 200° C. and 500° C.; small grain size and high 25
stability of grain size up to 500° C.; freedom from ex
hours’ duration
Z
at 450° C. at
stress of
r
cessive intercrystalline cavitation; high creep strength at
low stresses at the highest operating temperatures and
Parent Mg.Zr
Alloy A_____
Alloys used for cans in natural uranium reactors must 30
also possess very low neutron absorption cross-sections
Alloy 1 ______ __
good weldability.
and for this reason magnesium is the most important
metal to form the main constituent of any alloy used.
Any alloying elements used must be such that the neutron
absorption cross-section of the resulting alloy is adequate
ly small. Magnesium alloys which have been considered
Creep tests under more severe conditions at 50 p.s.i.
and 500° C. show that alloy (2) is superior to alloy (1)
35 and also to alloy (B) of similar Mn and lower Zr content,
even when the latter alloy was tested at a lower stress.
up to now have been those in which the main alloying
constituent is approximately 1% aluminum, magnesium
alloys containing 0.5% zirconium, and those containing
Composition,
Secondary creep
percent;
40
rate at 1,000
Stress,
0.5% zirconium and 0.5—1% zinc.
p.s.i. hours’ duration
at 500° C.,
The two alloys of magnesium with 0.5% zirconium, and
strain/hour
magnesium with 0.5 % zirconium and 0.5%-1% zinc have
many properties which make them suitable for reactor
24
15
1
cans with the exception that their creep strength at high
27
5
temperatures of the order 500° C. is insu?iciently high.
I have found that a small quantity of manganese al
loyed in magnesium with zirconium produces an alloy
The above data demonstrate that Mg—~Zr——Mn alloys
with high creep resistance, yet still possessing the other
containing 0.6% and 0.7% Zr are superior to the parent
desirable properties which are known to exist in binary
Mg-0.6% Zr alloy. At Mn levels of approximately 0.1%
magnesium-zirconium or ternary magnesium-zirconium
and approximately 0.25%, the data also show that con
zinc alloys. These improved alloys are basically single
tents of Zr of 0.6% and 0.7% respectively give higher
phase alloys, which at high temperatures do not exhibit
creep strengths than similar alloys containing less than
precipitation hardening which is usually associated with
0°
creep resistance.
55
An alloy according to the invention consists of zir
conium, magnesium and manganese, the proportions, by
weight, in the alloy being 0.5—l.0% Zr, 0.05—0.5% Mn,
and the remainder magnesium.
It is known that the useful liquid and solid solubility 60
of Zr in Mg to form a single phase alloy is about 1.0%,
above which percentage a zirconium precipitate is present
in the ?nal alloy. Also manganese has a limited liquid
and solid solubility in magnesium, such that if the amount
present in a binary alloy exceeds about 0.5% an undesir 65
able precipitate is present in the alloy, which may lead
to embrittlement.
If Zr and Mn are both present in an
Mg alloy, each of the two elements limits the solubility
of the other, Le. a small Mn addition of a few tenths
of 1% reduces the solubility of Zr to less than 1.0%. 70
The incorporation of Mn in the manufacture of Mg~Zr
alloys therefore necessitates the reduction of the Zr con
or equal to 0.5% Zr.
The following test data show that alloys (1) and (2)
possess a small grain size, free from excessive growth at
500° C., and exhibit adequate tensile ductility at 200° C.:
Average
grain '
Initial diameter in
average
microns
grain diamafter
eter in
annealing
microns
500 hours
Alloy
at 500° C.
Parent Mg.Zr ______ __
tensile
Percent
tensile
elongation
at fracture
when
strained at
0.1% per hr.
at 200° C.
at 200° C.
97
77
_ __
25
35
49
41
Alloy (2) ___________ __
37
60
85
41
Alloy (1) _ _ _ _ . _ _ _
32
Percent
elongation
at fracture
when
strained at
1% per hr.
76
What I claim is:
1. An alloy consisting of magnesium, zirconium and
3,071,4e2
4
3
manganese, the proportions, by weight, of the constituents
of‘the alloy being 0.6 to 0.7% zirconium, 0.1 to 0.27%
manganese, and the remainder wholly magnesium except
for unavoidable impurities.
2. An alloy consisting essentially, by weight, of zir
conium 0.6%, manganese 0.1%, and the remainder mag
nesium except for unavoidable impurities.
3. An alloy consisting essentially, by weight, of zir
conium 0.7%, manganese 0.27%, and the remainder
magnesium except for unavoidable impurities.
References Cited in the ?le of this patent
FOREIGN PATENTS
806,104
Great Britain _________ _- Dec. 17, 1958
OTHER REFERENCES
“In?uence of Zirconium upon the solidi?cation of
Magnesium Alloys and Some of the Properties of Mag
nesium Alloys Containing Zirconium,” by Franz Sauer
wald, Zeitschrift fiir Metallkunde, vol. 40, 1949, pp. 44
and 45 .